There is always something that goes wrong at cons for me, but this one is probably the worst:

I joined up with a friend and her friends for a con (sharing car, tents, etc.). They didn't exactly live where I live so driving back would have been a slight detour - so when I met some people that were from my city and apparently had a car too I mentioned to my friend that I might go with them for convenience.
The last day I spoke to the people I met again and it turns out there not driving to my city and all, so that wouldn't work out. I didn't think it was a big deal at the time.
My friend and I weren't really glued together because we were interested in different stuff on the con, so we agreed to a meeting place at a certain time when we would leave. When I got there and waited very long she wasn't there, I went to staff to get them to call her name over the speakers but she didn't show up. My cell phone didn't have any batteries at the time so I couldn't even call her!

After a while of hanging around the meeting place I finally got scared that she had left without me and went back to the camping grounds... and they had left.

So there I was, stranded in a strange city, with no money, no friends and no cell phone. I can safely say I was pretty close to a nervous breakdown, but I remembered that you can take the train and pay the fee for fare dodging later if you can't afford the ticket, so I thought I'd just try that and explain the staff my issue so they would let me stay on the train.

At the station I talked to the information lady and she sent me to the police (I hadn't even thought of that, silly me...) where I just broke down and cried a lot until the nice officer realised I could charge my cell phone at one of their stations, so we did that and then he called my friend.
They were already far out of the city, but turned around to gather me up. The friends of my friend were pissed at ME for some reason because now it would take them longer to get home.

They left because they thought I had gone with the other people, even though at no point did I say it was a sure thing. Her friends never liked me so my guess is that they made her think of me like a person that would just vanish without a word and ditch my friend just because I have a new lift...